Fastening arrangement for disposable diapers

ABSTRACT

A disposable diaper of the type having an impervious thin film backing is provided with integral fasteners comprising narrow strips of pressure-sensitive tape characterized by particularly advantageous properties. The tape has an adhesive mass strength of over 400 gms. per 3/4 inch width, a tensile strength in the long direction of the strip of at least 10 lbs. per inch of width, and an Elmendorf tear of at least 150 grams in the cross direction of the strip. One end of the strip is attached to the thin film backing of the diaper and adheres thereto so firmly that it will tear a 1 mil thick film rather than release. The other end of the strip extends beyond the diaper edges and is covered with a protective release sheet which adheres to the adhesive with an attachment force of from about 50 to about 300 gms. per 3/4 inch of width. This latter force is sufficient to retain the protective sheet on the strip during processing and handling but will permit stripping the sheet off the adhesive without damaging the adhesive, the film backing, or the strip itself when the diaper is ready for use.

United States Patent [72] Inventor Dan D. Endres Neenah, Wis. {21] Appl.No. 848,995 [22] Filed Aug. 11, 1969 [45] Patented Dec. 28, 1971 [73]Assignee Kimberly-Clark Corporation Neenah, Wis.

[54] FASTENING ARRANGEMENT FOR DISPOSABLE DIAPERS 8 Claims, 5 DrawingFigs.

[52] U.S. Cl 128/287, 1 17/122 F [51] 1nt.Cl. A611 13/16 [50] Field ofSearch l28/l55156, 153,169,284, 287, 296; 117/122 P [56] ReferencesCited UNlTED STATES PATENTS 2,714,889 8/1955 Chambers 128/284 X2,721,550 10/1955 Banff 128/156 2,834,347 5/1958 Connally 128/2843,026,217 3/1962 Hechtman et al. 117/122 X 3,026,241 3/1962 Hechtman eta1 117/122 X Primary ExaminerCharles F. Rosenbaum Attorneys-Daniel .1.Hanlon, Jr. and Raymond J. Miller ABSTRACT: A disposable diaper of thetype having an impervious thin film backing is provided with integralfasteners comprising narrow strips of pressure-sensitive tapecharacterized by particularly advantageous properties. The tape has anadhesive mass strength of over 400 gms. per /4 inch width, a tensilestrength in the long direction of the strip of at least 10 lbs. per inchof width, and an Elmendorf tear of at least 150 grams in the crossdirection of the strip. One end of the strip is attached to the thinfilm backing of the diaper and adheres thereto so firmly that it willtear a 1 mil thick film rather than release. The other end of the stripextends beyond the diaper edges and is covered with a protective releasesheet which adheres to the adhesive with an attachment force of fromabout 50 to about 300 gms. per inch of width. This latter force issufficient to retain the protective sheet on the strip during processingand handling but will permit stripping the sheet 05 the adhesive withoutdamaging the adhesive, the film backing. or the strip itself when thediaper is ready for use.

III II II III! II III FASTENING ARRANGEMENT FOR DISPOSABLE DIAPERSBACKGROUND OF THE lNVENTION In the manufacture of disposable diapershaving an impervious thin film backing such as polyethylene, it ishighly desirable to provide a positive fastening means other than theoldfashioned safety pin commonly used for that purpose. There is a needfor improved fastening, both from a safety and from a conveniencestandpoint. In addition, it is desirable that such fastener be anintegral part of the garment and that an economical method of attachmentduring manufacture be devised.

It has been suggested that strips of ordinary pressure-sensitive tapewould serve this purpose. However, most conventional tapes of this typedo not have a sufficiently aggressive adhesive to remain adhered to thesurface of polyolefin'film such as polyethylene during normal handling.The problem is further aggravated when an embossed film is used toprovide more attractive feel and appearance attributes. Consequently,when ordinary tapes are used for such attachment strips, the stripsfrequently become detached prematurely and are lost before the diaper isready for use. In addition, once the diaper is in place on the baby, ifthe adhesive does not adhere firmly, the fastening strip may come looseand therefore be ineffective. When tack is increased to overcome thesepremature detachment problems, another problem arises in trying toprovide a suitable protective release sheet for temporarily covering theadhesive on the unattached half of the fastening strip.

Conventional release sheets for covering pressure sensitive adhesivesare designed for easy release. As a result, these sheets tend to becomedisplaced prematurely during handling of the diaper, uncovering thepressure-sensitive mass and causing it to stick inadvertently to a wrongportion of the diaper or to an adjacent diaper in a package, whereuponthese diapers may be rendered useless. If the release sheet is designedwith sufficient adherent power to stay in place prior to using thediaper, it is difficult to remove the sheet without tearing the otherend of the strip from the diaper backing, or causing transfer ofadhesive to the protective strip, or rupturing the tape itself. If theprotectivesheet has a release agent applied on its contact surface toalleviate this problem, the sheet may release too easily, causing thesame problems mentioned above, or the release agent may destroy thepressuresensitive nature of the adhesive upon aging. It is highlydesirable, therefore, to provide astrip of tape for diaper fasteningpurposes in which one end adheres firmly to the film backing of thediaper, and the free end lends itself to easy release from a protectivecover strip without destroying the adhesive power of thepressure-sensitive mass.

With this invention there is disclosed a pressure-sensitive tapefastener strip for film-backed diapers which does adhere to the filmbacking with sufficient firmness to insure against displacement innormal handling and which is provided with a protective cover sheet thatcan be removed from the portion of the tape it covers without damagingthe tape strip, the adhesive mass, or the diaper.

SUMMARY OF THE INVENTION Pressure-sensitive tape strips normally foundsuitable for use with diapers usually have awidth of from about l inchto 94 inch and a length of about 2% inches to 3 inches. These tapes areordinarily supplied in the narrow width rolls and cut to the requiredlength for application to the diaper. In such cases the highest tensilestrength of the tape runs in the lengthwise or machine direction of thetape roll, and the highest tear strength runs in the crosswise ormachine direction of the tape roll. Accordingly, many common tapespecifications will meet the required minimum strengths in tear andtensile as specified herein if used in the normal manner. However, iftapes with Widths'set forth above are used in the machine production ofdiapers it means that the tape must be applied transversely to themovement of the diaper through the machine, requiring complicatedindexing mechanisms and intermittent stop motions in the machineoperation. The use of such complicated machinery would call for anincrease in capital expenditure, and the intermittent operation wouldresult in increased cost of operations, neither of which is desirable.

In accordance with this invention, it has been found that by utilizing atape stock whose width is equal to the length of the strip required,i.e., 2% inches to 3 inches, and by cutting narrow strips from thiswider tape stock, i.e., 9i inch to 34 inch, the tape can be applied fromrolls of tape arranged to turn in the same direction the diaper ismoving through the machine. Application to the diaper, therefore, isgreatly facilitated, the machine may be operated continuously withoutstop motion, and the capital expenditures are minimized. However, whentape is applied in this fashion, tear strength across the narrowdimension of the resulting strip is normally poor and tensile in thelong dimension of the resulting strip is also poor, as might beexpected. Ordinary tape, therefore, cannot be used, and

special attention must be given to providing higher tear and tensileproperties. In this regard, it has been found that wide tape stocks witha machine direction tear of at least 150 gms. (this is the crossdirection of the tape strip) and a tensile strength of at least 10 lbs.per inch of width in the cross direction (this is the long direction ofthe tape strip) is suitable.

In addition to having the above requirements with respect to tensile andtear, the tape must have sufficient adhering power to the surface ofpolyethylene or similar film used for the diaper backing so that it doesnot release prematurely. An adhesive mass strength of at least 400 gramsper 5 inch width has been found suitable. This characteristic isdetermined by applying the tape to a smooth polyethylene surface withpressure from a steel roll 1% inches wide, 4.0 inches in diameter, andweighing 4% pounds, and then measuring the stripping force required.

-A tape having such tack or adhering strength will tear a polyethylenefilm of 1 mil thickness rather than release therefrom. Film used fordiapers usually is 1 mil thick or less,

. although some thicker specifications have been used.

Pressure sensitive adhesive masses, including natural rubbers and/orsynthetics, can be formulated by known means by persons skilled in theart, to achieve a tack of the required degree. Tack can also be improvedby making the polyethylene surface itself more acceptable of adhesivesapplied thereto, by treating the surface with corona discharge or bychemical or physical modification, also well known in the art.

Still another requirement is to provide a protective release sheet forthe unattached portion of the tape strip which will stick to theadhesive during normal handling but will readily release therefrom whenready to apply the diaper. Conventional planar surface sheets having arelease surface, or treated with a release agent, were generally foundto pull away too easily, and such sheets tended to fall off prematurelyduring processing or handling. Planar sheets of polyethylene'used asprotective covers were found to adhere tightly to the tape strip havingthe higher adhesive mass strength as set forth above, but could not beremoved without damage to the strip or diaper. However, if thepolyethylene protection sheet is provided with raised embossments oflimited area and applied to the adhesive in a manner such that only theraised embossed portions contact the adhesive, the effective peelingwidth and concomitant adherence is reduced to an extent that theembossed strip will remain attached during processing, yet may beremoved when necessary. By peeling width is meant the width of thecontact area of the embossed polyethylene to the pressure sensitiveadhesive transverse to the direction of peeling.

When the raised embossments comprise 33% percent of the surface area incontact with the pressure sensitive adhesive mass, and the individualcontact points have a peeling width of about l.5.mm., attachment forceof a tape normallyhaving but contact of the individual embossments isreduced to about.

0.2 mm. peeling width, attachment force is reduced to about 50 g. per 34inch of width. When the raised area embossments with the 0.2 mm. peelingwidth are placed closer together so that they comprise 50percent of thesurface area, the attachment force is in the neighborhood of I50 g. perinch width.

In summary, the invention comprises a film-backed disposable diaper withimproved integral fasteners comprising strips of pressure-sensitive tapeattached to the film backing at opposite edges of one end of the diaper.One end of each strip is attached to the film backing by means of thepressure sensitive adhesive which is formulated to have an adhesive massstrength of over 400 g. per inch of width. The other end of the stripextends beyond its respective edge of the diaper and is covered with aprotective release sheet which adheres to the pressure sensitiveadhesive with an attachment force of from about 50 g. to about 300 g.per W4 inch of width. The reduced attachment force of the protectiverelease strip may be obtained by providing a polyethylene sheet withraised embossments of limited area to contact the adhesive. The tapestrip has a tensile strength in its long direction of at least lbs. perinch of width, and an Elmendorf tear of at least 150 grams in the crossdirection of the strip.

Accordingly the primary object of the invention is to provide animproved integral fastening device for film-backed disposable diapers.

Another object is to provide a fastening tape for diapers with a releasesheet of improved function.

Still another object is to provide a fastening tape for diapers whichmay be more economically applied during manufacture.

These and other objects will become apparent by reference to thefollowing specification and drawings wherein there are described variousselected embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the back sideof a disposable diaper showing a pair of pressure-sensitive tape stripsaffixed to the film backing near the side edges of the diaper at one endthereof.

FIG. 2 is a partial plan view of the front side of the top portion ofthe diaper of FIG. 1.

FIG. 3 is a section taken along lines 33 of FIG. 2.

FIG. 4 is a perspective view of a suitable protective cover sheetshowing a typical embossing pattern for contact with the pressuresensitive adhesive.

FIG. 5 is a perspective view showing another typical embossing patternfor a protective cover sheet with a selected portion thereof greatlyenlarged.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The disposable diaper havingthe improved fastening devices of this invention applied thereon may beof conventional construction comprising a main absorbent pad 12consisting of wood pulp fluff, layers of cellulose wadding, absor-- bentcotton fibers, and the like. Pad 12 has a thin impervious film backing14, which typically may be pigmented and embossed 1 mil polyethylene.The outer surface of the film backing l4 may-also be treated by coronadischarge or the like to provide a surface more receptive to adhesive.Film backing 14 is usually at least coextensive with the pad butpreferably extends around the edges of the pad and partially overlapsthe top of the pad. The top surface of pad 12 is covered with a fluidpervious sheet 16 which is usually of'nonwoven construction and may behydrophilic or hydrophobic. Cover sheet 16 may be attached to filmbacking 12.either on top of the overlapping edge as shown in .FIG: 3 orunderneath the overlapping edge as shown in FIG. 3 or underneath theoverlapping edge. In other constructions cover sheet I6 may extendaround the sides of pad I2 and be attached on the bottom side of thediaper either over or under film backing 12, or cover sheet 16 and filmbacking 12 may extend beyond the diaper edges and be heat sealedtogether.

Near one end of the diaper and at opposite edges thereof are attachednarrow strips 18 of pressure-sensitive tape with one endextending'beyond the respective edges of the diaper with the pressuresensitive adhesive coating 21 on the surface of these extensions coveredby a protective cover sheet 20 which preferably is embossed polyethyleneas further described below. The cover sheet is usually wider and longerthan the tape to provide a convenient handle for removal. The inwardlydisposedv end of the cover sheet preferably extends over the face of thediaper.

Typical embossing patterns for the protective sheets are shown in FIG. 4and FIG. 5. InFIG. 4 the face of cover sheet 20, which is about 6 milsthick, comprises a plurality of raised diamond shaped embossments orland'areas 22 separated by intersecting sets of parallel channels orgrooves 24 and 26. It is this face of the cover sheet 20, andconsequently only raised embossments 22 which contact adhesive 21 whensheet 20 is in place, and which provide the effective peeling width.Typical dimensions of the diamonds in the pattern shown in the drawingare about 1.5 mm. from point to point of the narrow dimension and 2.5mm. from point to point of the wide dimenslon.

In FIG. 5, the face of the cover sheet 20a comprises a plurality ofparallel raised lines 28, intersected by a plurality of parallel lines30, which lines 30 are in a lower plane than lines 28, and still deeperdiamondshaped embossments 32 which the intersecting lines 28 and 30define. Typical width dimensions of the raised lines 28 is about 0.2 mm.When the face of this cover sheet is placed in contact with adhesive2l'only the raised lines 28 adhere thereto, and the effective peelingwidth of the individual lines is 0.2 mm.

The pressure sensitive adhesive mass 21 is compounded from natural orsynthetic rubber or the like, by methods known to persons skilled in theart, to have an adhesive force of at least 400 g. per 74 inch of width;i.e., 400 g. of force are needed to strip a 182 inch wide tape havingsuch an adhesive coating from a smooth polyethylene surface when appliedas previously defined. When tape with such a coating is applied to 1 milthick polyethylene film, it will normally tear the film rather thanrelease therefrom.

The preferred base sheet material for the tape strip is alatex-impregnated paper having a high delamination resistance and highinternal or edge tear. Base sheets of this type are generally defined inassignees US. Pat. Nos. 3,026,241; 3,026,217; and 3,066,043. Such tapesgenerally comprise a sheet of cellulose fibers impregnated with anelastomeric polymer such as polymers and copolymers of conjugateddienes, natural rubber, and the like. Other suitable base sheets for thetape including nonfibrous films such as vinyl plastics, cellophane,cellulose esters, polyethylene terephthalate or similar polyesters, andthe like, may be employed as long as they have the tensile and edge tearcharacteristics mentioned above. Also usable are woven and impregnatedfabrics such as cotton fabric, synthetic fiber fabrics, glass fabricsand the like, and nonwoven and impregnated fibrous webs such as cardedwebs of natural fibers, self-bonded synthetic fiber felts and the like.However, the invention is particularly useful in connection with themore economicahtype tapes in which the base sheet is made from paperstock which has been treated with a saturant to unify the fibers andwhich imparts internal strength and resistance to delamination.

If such latter tapes are used in the 2% inches to 3 inch widthsmentioned earlier and cut into 2% inch to inch strips for application tothe diaper, the fibers in the tape are generally aligned transverse tothe cut strips and the major tensile strength is in the cross directionof the cut strips, accordingly care should be taken to select a tapewhich meets the minimum strengths previously mentioned, i.e., anElmendorf tear of at least 150 g. in the width or cross direction of thestrip and a tensile strength of at least lbs. per inch of width in thelong direction of the strip.

A suitable protective cover sheet for the pressure sensitive masspolypropylene.- the ends of the strip which extend beyond the edge ofthe diaper is embossed polyethylene film of from about 3 to 6 milsthick. Other embossments besides the diamond pattern configurationsshown in the drawings may also be used. However an importantconsideration is that the transverse width of of the raised portions ofthe embossments does not exceed about 2.5 mm. and that the area of theraised embossments does not exceed 50 percent of the total surface areaof the sheets, so that the peel force required will not exceed about 300grams per it inch of width. Other fairly rigid films such aspolypropyelene. polyesters, and polyvinyl chloride may also be used asthe protective cover sheet.

Extensive tests under actual use conditions were made of diapers withtape strips having an adhesive mass with an attachment strength tosmooth polyethylene of 400 grams per /4 inch width, an Elmendorf tear of150 grams in the narrow direction, and a tensile in excess of 10 lbs.per inch of width. Results indicated a failure rate of less than 2percent. However upon further analysis these failures were attributed tothe inadvertent coating by the mother of the pressure-sensitive masswith powder or lotion rather than to inadequate attachment strength.

Additional tests also indicate that the Elmendorf tear strength of 150grams is necessary in the narrow direction of the strip to preventlarger babies from tearing the tape strips themselves.

What is claimed is:

1. In a disposable diaper of the type combining an absorbent pad with afluid pervious cover and a fluid impervious thin film backing to whichare attached a pair of integral fasteners comprised of narrow strips ofpressure-sensitive tape, the improvement in which said tape comprises acellulose fiber paper sheet impregnated with a unifying and strengthimparting saturant with the fibers in said sheet aligned transverse tothe length of said strips; in which said tape has a tensile strength inthe long direction of the strip of at least l0 lbs. per inch of widthand an Elmendorf tear in the cross direction of the strip of at leastgrams; and in which the pressure sensitive adhesive of said tape has anadhesive mass strength of more than about 400 grams per it inch ofwidth; one end of each of said strips being disposed in contact with andattached to said film backing by said adhesive near opposing edges ofone end of said diaper and the adhesive surface of the other end of eachof said strips being covered by a protective cover sheet having anattachment force to the adhesiveof between about 50 and 300 grams per )6inch of width.

2. The diaper fastening arrangement of claim 1 in which said filmbacking is about 1 mil thick and the adhesive attachment of said stripthereto is such that it will tear said film backing without releasingtherefrom when sufficient force is applied thereto.

3. The diaper fastening arrangement of claim I in which the free ends ofthe tape strip extend beyond the respective edges of the diaper.

4. The diaper fastening arrangement of claim 3 in which a portion of theprotective sheet covering the free ends of the diaper extends inwardlyover the face of the diaper.

5. The diaper fastening arrangement of claim 1 in which said cover sheethas raised embossments on the surface and said embossments are incontact with said adhesive.

6. The diaper fastening arrangement of claim 5 in which the raised areaof said embossments comprise from about one third to about one half ofthe surface area of said film and the peeling width of said embossmentsrange between about 0.2 and 2.5 mm.

7. The diaper fastening arrangement of claim 5 wherein said protectivecover sheet comprises a plastic film of from about 3 to 6 mils inthickness.

8. The diaper fastening arrangement of claim 7 in which said plasticfilm is selected from the group consisting of polyethylene,polypropylene, polyester, and polyvinyl chloride.

is i i

2. The diaper fastening arrangement of claim 1 in which said filmbacking is about 1 mil thick and the adhesive attachment of said stripthereto is such that it will tear said film backing without releasingtherefrom when sufficient force is applied thereto.
 3. The diaperfastening arrangement of claim 1 in which the free ends of the tapestrip extend beyond the respective edges of the diaper.
 4. The diaperfastening arrangement of claim 3 in which a portion of the protectivesheet covering the free ends of the diaper extends inwardly over theface of the diaper.
 5. The diaper fastening arrangement of claim 1 inwhich said cover sheet has raised embossments on the surface and saidembossments are in contact with said adhesive.
 6. The diaper fasteningarrangement of claim 5 in which the raised area of said embossmentscomprise from about one third to about one half of the surface area ofsaid film and the peeling width of said embossments range between about0.2 and 2.5 mm.
 7. The diaper fastening arrangement of claim 5 whereinsaid protective cover sheet comprises a plastic film of from about 3 to6 mils in thickness.
 8. The diaper fastening arrangement of claim 7 inwhich said plastic film is selected from the group consisting ofpolyethylene, polypropylene, polyester, and polyvinyl chloride.